distribution, diversity and conservation of the genus ...

DISTRIBUTION, DIVERSITY AND CONSERVATION OF THE GENUS ALOE IN KENYA Author(s): Emily Wabuyele, Charlotte Sletten Bjorå, Inger Nordal, and Leonard E. Newton Source: Journal of East African Natural History, 95(2):213-225. 2006. Published By: Nature Kenya/East African Natural History Society DOI: http://dx.doi.org/10.2982/0012-8317(2006)95[213:DDACOT]2.0.CO;2 URL: http://www.bioone.org/doi/full/10.2982/0012-8317%282006%2995%5B213%3ADDACOT %5D2.0.CO%3B2

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Journal of East African Natural History 95(2): 213–225 (2006)

DISTRIBUTION, DIVERSITY AND CONSERVATION OF THE GENUS ALOE IN KENYA Emily Wabuyele East African Herbarium, P.O. Box 45166, Nairobi 00100, Kenya and Department of Biology, University of Oslo, P.O. Box 1045, 0316 Oslo, Norway [email protected] Charlotte Sletten Bjorå, Botanical Garden & Museum, University of Oslo, P.O. Box 1172 0318 Oslo, Norway [email protected] Inger Nordal Department of Biology, University of Oslo, P.O. Box 1045, 0316, Oslo, Norway [email protected] Leonard E. Newton Department of Plant & Microbial Sciences, Kenyatta University P.O. Box 43844,Nairobi, 00100, Kenya [email protected]

ABSTRACT The genus Aloe is common in Kenya, with about 60 taxa recognised. Observations from this study indicate that most of the taxa have a restricted distribution, with only Aloe secundiflora var. secundiflora being widespread in the country. The diversity patterns indicate a high concentration of taxa in three areas that are identified as Aloe hot spots and thus of high priority for conservation of the genus: The Kulal–Nyiro– Ndotos–Marsabit area in the north, the Taita–Shimba Hills zone to the southeast and the Naivasha–Baringo area in the Rift Valley. Most of the microendemic taxa are concentrated in the Kulal complex, a few in the Taita complex while the Naivasha complex includes mainly the widespread ones. Based on the computed Extent of Occurrence (EOO) and the threats to individual populations of endemic taxa about 36% were assessed as being Critically endangered, 32% as Endangered, 12 % as Vulnerable, 12% as being Near Threatened and 8% of Least Concern, according to IUCN Red Listing Criteria. Key words: mapping, endemic, extent of occurrence, species richness, terrain diversity

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E. Wabuyele, C. Sletten Bjorå, I. Nordal & L.E. Newton

INTRODUCTION The genus Aloe L. is distributed on the African mainland south of the Sahara, on Madagascar, the Arabian Peninsula and on several islands in the Indian Ocean, including Socotra. The main centre of diversity for the genus is South Africa, with about 120 taxa. Other important centres of diversity are eastern Africa and the Island of Madagascar. A complete survey of taxonomic diversity for the genus Aloe over its geographical range is given by Newton (2004a). Aloes are known to occur in a wide range of habitats at altitudes that vary from sea level to 3300 m. The physiological adaptations in aloes, like sunken stomata and a heavy wax cover on the leaf cuticle, make the plants particularly fitted for xeric habitats. The plants also possess traits that make them tolerant to disturbance, particularly the spiny leaves and bitter taste, which are deterrent to browsing. According to Newton (2004a), aloes are rarely dominant in the ecological sense, except in places where vegetation is sparse, with aloes being the only large plants. Kenya covers a total land area of 582 646 km2 between latitudes 5oN-5oS and longitudes o 34 -41oE, in northeastern Africa. Altitude varies from sea level (the Indian Ocean) to 5194 m on Mount Kenya. The country is bisected by the eastern Great Rift Valley of tertiary volcanic origin. The country’s climate is variable and mainly influenced by altitude, and the distance from the Indian Ocean in the east or from Lake Victoria in the west (Lucas, 1968). Rainfall is scanty and unreliable in most areas, with only 20% of the country receiving 500 mm or higher per year. Phytogeographically the zone between the Rift Valley and the coastal belt belongs to the Somalia Masai Regional Centre of Endemism (RCE) according to White (1983). This is an extensive region that is only occasionally broken by the Afromontane archipelago-like RCE to which the highlands on both sides of the Rift Valley belong. The Western part of the country belongs to the Lake Victoria Regional Mosaic (RM) and the coastal strip to the Zanzibar-Inhambane RM. The coastal forests and some of the isolated mountains in southeastern Kenya are part of the Eastern Arc and Coastal Forests Hotspot (Myers et al., 2000). A recent reappraisal of the global hotspots by Conservation International recognised second biodiversity hotspots in this zone, namely the Eastern Afromontane Hotspot (Mittermeier et al. 2005). The vegetation of Kenya is highly influenced by the wide range of altitudes and variation in climate. Like in many other countries in sub-Saharan Africa, the natural vegetation is degrading fast and conversion of land for agriculture reduces pristine habitats. The central highlands of Kenya are characterised by high population density, with much of the land under cultivation. The north and east are covered mainly by dry bushland and grassy plains. The west is mostly cultivated with a few forest remnants and some swamps along Lake Victoria while the coastal belt is dominated by mangroves in inter-tidal zones and estuaries and along creeks, and some dry forest patches (Marshall, 1998). According to recent estimates, Kenya is home to a total of 6500–6700 vascular plant species, about 5% of which are endemic to the country (Marshall, 1998; Beentje & Smith, 2001; Simon Kang’ethe, pers. comm.). Since the publication by Reynolds (1966), in which about 30 Kenyan Aloe taxa were listed, there have been considerable gains in the documentation and knowledge of the genus in the country. The distribution and taxonomy of Kenyan aloes are well studied at alpha-taxonomic level (Carter, 1994; Newton, 2001) and chemical profiles of some taxa (Viljoen et al., 1998, 1999, 2001; Reynolds, 1985, 1986,

Distribution, diversity and conservation of Aloe in Kenya

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2004). Newton (1996, 2004b) has exemplified the multi-use value of some aloes to local African communities. Of the more than 80 taxa (species, subspecies and varieties) of the genus Aloe recognized in the East African Flora, at least 59 occur in Kenya. This number is considerably higher than other country estimates in the region. For instance, the number of taxa known so far in Eritrea and Ethiopia is 43, in Somalia 33, in Tanzania 40, and in Uganda 16 (Carter, 1994; Lavranos, 1995; Newton, 2001; Sebsebe et al., 2001). The Kenyan richness in Aloe taxa is emphasized further when translated into species densities per million km2, which amounts to 101 taxa for Kenya, 68 for Uganda, 52 for Somalia, 42 for Tanzania and 35 taxa for Eritrea and Ethiopia. In traditional local communities, the medicinal use of aloes was at a sustainable level. During the last century, however, population pressure (both human and livestock) has led to the increased destruction of plants in the wild. The problem is exacerbated by international demand for and trade in aloe products, requiring the harvesting of tons of plants in the wild in order to gather the leaf exudates that are processed into the commodity known as ‘aloe bitters’ (Kihara et al., 2003). The taxa that are reported to be harvested in Kenya include Aloe secundiflora, Aloe turkanensis and Aloe scabrifolia (Oketch, 1991). Following a 1986 presidential decree against exploitation of wild-growing aloes (Nyamora, 1986), the Kenya Wildlife Service, which is the national body that is charged with the protection and conservation of the country's biodiversity, has maintained a ban on the commercial exploitation of wild-growing aloes. Additional restrictions on international trade in species of Aloe are imposed by the Convention on International Trade in Endangered Species (CITES), to which Kenya is signatory (CITES, 2006). To a large extent, deficiencies in the national wildlife conservation policy have been cited as an impediment to Aloe conservation in Kenya (KAWG, 2004). The problem is further compounded by inadequate substantiation on the data available on the genus. This paper aims to enhance the conservation of aloes in Kenya by presenting information in a direct and illustrative way. Geographical Information System (GIS) technology was used to display the spatial patterns of aloe distribution and diversity based on point (locality) data. On the basis of distribution and diversity patterns, Aloe ‘hot spots’ were identified. Furthermore, a preliminary red data listing for individual taxa was done and appropriate conservation priorities are proposed. It is hoped that these will nurture the sustainable utilization of the genus by promoting monitoring initiatives for wild-growing populations of aloes.

MATERIALS AND METHODS Benchmark publications on the genus (Reynolds, 1966; Carter, 1994; Newton, 2001, 2004a) were consulted to identify all Aloe taxa with a Kenyan distribution, their habit, habitats and altitudinal ranges at sites of occurrence. Using the BRAHMS software (Botanical Research and Herbarium Management Systems, The BRAHMS Project, Department of Plant Sciences, University of Oxford), details of about 850 specimens of Kenyan aloes were captured from the East African Herbarium (EA) and the Herbarium at the Royal Botanic Gardens, Kew (K). In cases where specimen localities were not geo-referenced, the gazetteer of collecting localities by Polhill (1988) was consulted. It was inevitable that in many cases, several specimens were linked to a single reference point. Extensive field surveys were carried out in

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most parts of the country to verify known populations and hunt for unknown ones. It must be emphasized that some of the recorded localities may have been destroyed or reduced, as is the case of the population at the type locality of A. ballyi in Taita Taveta District (Newton, in press). Digital maps of Kenya were obtained from the Norwegian Institute for Nature Research (NINA) and the National Museums of Kenya (NMK). Using Arc View software version 3.3, latitude/ longitude values from the specimen database were plotted onto a country map that was subdivided into quarter (30ƍ × 30ƍ) degree square grids. Species richness (diversity) was inferred from simple grid diversity counts. Based on distribution records for the taxa, endemic taxa were filtered out and plotted on a separate map. Species rarity was deduced from total specimen and locality records for each species. Using the X-tools option for calculating polygon areas in Arc View, the Extent of Occurrence (EOO), was computed for taxa known from three or more data points. The EOO as defined by IUCN (2001) is the area contained within the shortest continuous imaginary boundary that can be drawn to encompass all the known, or inferred or projected sites of present occurrence of a taxon. In order to make red data assessments for the endemic taxa, we used our personal field knowledge of Kenyan aloes as a well as a status report by Newton (1995) to evaluate the levels of fragmentation of the species, their population sizes and trends and threats to their survival. In addition, botanists with first hand knowledge of the plants and their locations in the field, such as Stella Simiyu (SCBD / BGCI) and Quentin Luke (National Museums of Kenya) were consulted before reaching a status assessment.

RESULTS Distribution and species richness About 66% of the taxa occur in deciduous bushland/woodland vegetation, 14% in grasslands, while the remaining 20% inhabit edges of thickets, riverine woodlands, scrubland or rock outcrops. A wide range of altitudes is encountered, from sea level for Aloe massawana to as high as 2300 m for Aloe juvenna. Approximately 10% of the taxa are found at altitudes of between 0-500 m, 24% between 500-1000 m, 32% between 1000-1500 m, 24% between 1500-2000 m and 10% between 2000-2500 m. The entire distribution of the genus in Kenya was represented by 385 data points, collated from herbarium records in EA and K, published literature and field observations. The Aloe data points emerged in about 50% of the quarter degree squares (108 of the 219). Generally, there is positive correlation between the number of collections, taxonomic diversity and levels of endemicity per grid. With reference to the Equator, running approximately through the middle of the country, the southern half of the country contains more aloes than the northern half. Aloe secundiflora var. secundiflora is the most widespread taxon, represented by at least 57 data points (EOO = 136 287 km2). Most of the other taxa had restricted ranges or occurred in relatively small disjunct patches over their ranges. The ten most common/widespread Kenyan Aloe taxa are presented in table 1. Grid square diversity ranged between zero and nine taxa per square (figure 1). The highest grid diversity was registered in squares around the Taita–Taveta area (Somalia-Masai RCE). Grid square diversity of up to eight was recorded around the valleys and ridges within one degree north/south of the Equator and immediately flanking the Rift Valley. Within the Lake Victoria and western Kenya areas (Lake Victoria RM), grid diversity ranged between


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zero and six. The expansive North Eastern Province (Somalia Masai RCE) had the highest number of blank grid squares with occasional grid square diversity records of two to four, while the lowest levels of zero to two taxa were recorded in the West Pokot-Turkana areas. Table .1 Occurrence of the 10 most common aloes of Kenya based on computed values of EOO. Distribution (K1–K7) according to Polhill (1988). Taxon Aloe secundiflora Engl. var. secundiflora Aloe myriacantha (Haw.) Schult. & Schult.f. Aloe deserti A.Berger Aloe volkensii Engl. Aloe lateritia Engl. var. lateritia Aloe scabrifolia L.E.Newton Aloe dawei A.Berger Aloe kedongensis Reynolds Aloe ellenbeckii A.Berger Aloe lateritia Engl. var. graminicola (Reynolds) S.Carter

2 EOO (km )

Kenyan Distribution

136 287

K1, 3-7; not endemic

7

37 869

K3, 4,6,7; not endemic

18 9 13

14 9 10

26 130 23 518 20 833

K4, 6, 7; not endemic K6, 7; not endemic K4,6 7; not endemic

9 7 17 3 19

6 7 12 3 11

16 575 13 727 12 670 12 598 11 460

K1,4; endemic K5; not endemic K3-6; endemic K1, 4; not endemic K1, 3, 4-6; endemic

Data points 57

Total grid squares 36

9

Figure 1. Patterns of taxonomic diversity of the genus Aloe in Kenya. The numbers 0-9 refer to the total number of taxa recorded in each square.

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Patterns of endemicity The 25 Kenyan endemic taxa were represented by 35% of the total data points registered for the entire generic range, one third of which represented only two of the most common taxa. Most of the endemic taxa have restricted distributions, and are frequently known from only one data point (seven taxa, which accordingly may be denoted micro-endemics) or two data points (three taxa). It was therefore not feasible to compute EOO values for these (table 2, marked with * under EOO) as was done for taxa known from three or more data points. The computed EOO values for the endemics category shows Aloe scabrifolia to be the most widespread species. However, it is should be noted that A. scabrifolia (EOO = 16 575 km2) is a rare species and is far less abundant than for instance A. kedongensis (EOO =12 670 km2) and A. lateritia var. graminicola (EOO = 11 460 km2), respectively. The largest diversity of narrow endemic taxa was found in the northern half of the country (figure 2). Examples of such taxa include A. archeri, A. pustuligemma and A. kulalensis. Although peaking on the cells around Mount Kulal, it is apparent that several of the isolated volcanic formations neighboring the Chalbi Desert in this zone are part of this unique biodiversity-rich complex in the arid north. These include Mount Nyiru (2743 m), the Ndotos (2688 m) and Mount Marsabit (1828 m).

Figure 2. Patterns of endemicity of the genus Aloe in Kenya. The numbers 0-4 refer to the number of endemic taxa recorded in each square.

The South Eastern corner of the country (Taita–Shimba hills complex) exhibited moderate levels of endemicity, which also include some narrow endemic taxa such as A. penduliflora

Aloe amicorum L.E.Newton Aloe carolineae L.E.Newton Aloe classenii Reynolds Aloe juvenna Brandham & S.Carter Aloe ketabrowniorum L.E.Newton Aloe kulalensis L.E.Newton & Beentje Aloe lensayuensis Lavranos & L.E.Newton Aloe lolwensis L.ENewton Aloe multicolor L.E.Newton Aloe murina L.E.Newton Aloe powysiorum L.E.Newton & Beentje Aloe vituensis A.Baker. Aloe francombei L.E.Newton Aloe archeri Lavranos Aloe penduliflora A.Baker Aloe tugenensis L.E.Newton & Lavranos Aloe chrystostachys Lavranos & L.E.Newton Aloe nyeriensis Christian Aloe aageodonta L.E.Newton Aloe elgonica Bullock Aloe pustuligemma L.E.Newton Aloe ukambensis Reynolds Aloe lateritia Engl.var. graminicola (Reynolds) S.Carter Aloe kedongensis Reynolds Aloe scabrifolia L.E.Newton & Lavranos

Taxon

Total grid squares 1 1 2 1 1 1 1 1 1 1 2 2 2 2 4 2 5 7 3 3 4 5 12 9 6

Data points 1 1 2 2 1 2 1 1 1 1 2 2 4 4 7 7 7 13 5 6 5 10 19 17 9

12 670 16 575

2544 2625 3410 3687 4709 11 460

EOO in 2 ( Km ) * * * * * * * * * * * * 52 552 869 1029 2522

K3-6 K1,4

K1,3,4 K4 K3 K1 K4,7 K1,3,4-6

K1 K1 K7 K6 K1 K1 K1 K5 K1 K6 K1 K4,7 K3 K1, 3 K7 K1,3 K4

Distribution

Near threatened Vulnerable [B1ab(v)]

Near Threatened Least Concern Endangered [B1ab(iii)] Near Threatened Endangered [B1ab(iii)] Vulnerable [B1ab(iii,,v)]

Critically Endangered [B1ab, B2ab(iii)] Critically Endangered [B1ab, B2ab(iii)] Critically Endangered [B1ab+ B2ab(iii)] Critically Endangered [B1ab(v)+ 2ab(v)] Critically Endangered [B1ab, B2ab(iii))] Critically Endangered [B1ab(iii)+2ab(iii)] Critically Endangered [B1ab, B2ab(iii)] Critically Endangered [B1ab, B2ab(iii)] Critically Endangered [B1ab, B2ab(iii)] Least Concern Endangered [B2ab(iii) ] Endangered [(B2ab(iii)] Vulnerable (D2) Endangered [B1ab(iii) ] Endangered [B1ab(v) ] Endangered [B1ab(iii) ] Vulnerable (D2)

Proposed IUCN listing/criteria

Table 2 Extent of Occurrence for Kenyan endemic Aloe taxa and proposed IUCN (2001) Red list categories.

Distribution, diversity and conservation of Aloe in Kenya 219

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and A. classenii. Around the central Kenya Rift Valley complex, another peak of endemism is apparent, but mostly comprising the more widespread endemic elements such as A. kedongensis. The western Kenya area has the lowest endemicity level of one taxon only. Based on the distribution patterns, threats to populations and computed values of the EOO, the endemic taxa were evaluated against the IUCN (2001) criteria to assess their risk for extinction (table 2). Most of the taxa satisfied criteria for listing as Critically Endangered (36%), Endangered (32%), Vulnerable (12%) or Near Threatened (12%) while only two of them were assessed to be species of Least Concern (8%).

DISCUSSION The compilation and mapping of distributions based on point data has been recognized as the finest scale at which geographical ranges of taxa can be assessed (Peterson & Watson, 1998, Baillie et al., 2004). For individual entities, the EOO based on a combination of known records is an important predictor of levels of threat. This, however, has been shown to greatly overestimate occupancy within range (Corsi et al., 2000). It has also been shown that the use of a relatively small grid size enables detailed analysis of the topographical complex areas within a study area (Linder, 2001). Although uneven and incomplete sampling is a general limitation in the application of this approach (Küper et al., 2006), our data are based on documentation accumulated and collated over many years of research and specialist experience with the genus Aloe in East Africa in general and in Kenya in particular. The problem of sampling bias could be most significant for the remote North Eastern Province, where insecurity and a poor road network restrict access to large areas, a phenomenon that is not limited to this group of plants (Hepper, 1979; Beentje and Smith, 2001). Diversity in Kenyan aloes For a genus whose members possess leaf succulence and therefore tolerance to water stress, its presence/dominance on the Kenyan landscape (with 80% dry lands) is not surprising. The various Aloe life forms as outlined by Holland (1978) for mainland Africa and Madagascar are well represented in Kenya: miniature aloes (3%), solitary rosettes (12%), suckering rosettes (27%), pendulous plants (7%), sprawling plants (24%), erect shrubs (20%) and trees (7%). The distribution maps for the genus in Kenya show that taxa are spread more or less across the whole country. What is evident, however, is the fact that even within the same general geographical region some grid squares of exceptionally high species richness stand out from squares of generally low taxonomic diversity, a fact that may be attributed to uneven sampling or the existence of pockets of suitable habitats within generally unsuitable regions. Holland (1978) observed that aloes occur in all vegetation types, except in the equatorial rain forest, and that they grow best in areas of about 200–800 mm of rainfall per annum. The distribution of the Kenyan taxa corroborates these observations. Species diversity is highest in the Taita Taveta area in the south eastern corner with moderate amounts of rainfall that support woodland and bushlands. Low species diversity is observed in the Western Region, which receives high amounts of rainfall that support lush vegetation approaching the ‘rain forest’ type in some places.


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Evidently, extreme dryness/aridity as found in some localities in northern and northeastern Kenya is detrimental to Aloe diversity. As shown from the analysis here, species richness peaks around the Taita Hills to the south-east and the valleys and escarpments to the east and west of the Rift Valley around Naivasha-Nakuru-Baringo areas. These can be seen as ‘islands’ of aloe diversity that have in common a high diversity of terrain and habitats that jointly support varied life forms. This being the case, however, regions with ‘optimal’ ecological conditions for the genus include many widespread taxa as opposed to the rare/endemic ones (Fox & Fox, 2000). Extrapolated onto the phytochoria classification of White (1983), these data show the highest diversity of aloes in the relatively wetter parts of the Somalia-Masai RCE, and parts of the Zanzibar-Inhambane RM. The Lake Victoria RM has the lowest levels of Aloe diversity. Endemicity in Kenyan aloes Although most of the grid squares in the northern part of the country had no records of Aloe taxa, the majority of occupied squares registered one hundred percent endemicity, i.e. the one and only taxon recorded for a grid square occurs nowhere else. The elevated degree of endemicity in this part of the country climaxes in cells around Mount Kulal in which the highest national level of four endemic taxa is recorded. The significance of the northern half of Kenya as an area of Aloe endemicity is emphasized further by the predominance of microendemic taxa. Cox and Moore (2005) observed that the degree of endemicity is determined by two major factors, namely isolation and stability. This confinement of species to areas where they evolved may be due to physical barriers to dispersal (paleoendemics) or to the fact that they have only recently evolved and therefore not had time to spread from their centres of origin (neoendemics). It may also be due to the fact that the taxa have poor dispersal ability, or are adapted to surviving in specific environmental conditions and cannot compete outside their home range (Lovett & Friis, 1996). In general terms, the ecological conditions of the north and north-eastern region of Kenya are harsh. Rainfall is low to the extent that it only supports simple/impoverished vegetation gradients. However, Mount Kulal occupies a unique ecological position in the northern region. There is an abrupt topographical transition from the surrounding Lake Turkana (23 km away) at 370 m altitude to the highest peak of the mountain at 2116 m above sea level. In sharp contrast to the extremely harsh ecology in the neighbourhood, a range of habitats exist on Kulal that include desert, semi arid zone and a montane zone supporting rain forest (Hepper, 1979). The ecological setting of Mount Kulal and findings of elevated endemism are in line with observations on some Ethiopian geophyte taxa (Nordal et al., 2001). Viewed against the general ecological setting and the specific conditions on Mount Kulal and similar formations in northern Kenya, it seems logical to speculate that aridity, which is the most prominent selection pressure in northern Kenya, is responsible for the elimination of poorly adapted taxa of Aloe. This ensures low establishment rates, and the ensuing genetic drift as a result of isolation (by distance/altitude) enhances divergence in populations and taxa. This effectively leads to high prevalence of speciation events in northern Kenya as compared to other areas. In addition to this, the predictability of aridity in this zone probably confers environmental stability that offers larger opportunity for continuous terrestrial evolution while at the same time imposing stringent conditions of survival due to punishing arid conditions (Lovett & Friis, 1996; Hopper & Gioia, 2004).

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Conservation For the purpose of this analysis and conservation planning, we advance the following categorization in order of increasing species diversity and endemicity levels: 1) ‘Aloe Cold Spots’, centred on grid squares with diversity of zero to four taxa; 2) ‘Important Aloe Areas’, centered on grid squares with diversity of five to nine taxa or any square containing an endemic taxon; (3)‘Aloe Hot Spots’ (AHS), centred on grid squares with total diversity of more than five taxa and including one or more endemic taxa. It remains to be investigated whether the patterns of Aloe diversity can reliably be used to predict the distributions of similarly adapted plant groups of the country and the East African region in general. Based on the limited distribution and small values of the EOO, most Kenyan endemic taxa qualify for listing under the IUCN (2001) guidelines as indicated in table 2. In assessing the conservation status of the various taxa and their priority for conservation intervention consideration has been given to the threats to the populations, level of fragmentation as well as the level of use at the various locations. However, the categories accorded to the taxa here should be considered tentative pending formal validation by the relevant Red Listing Authorities.

CONCLUSIONS AND RECOMMENDATIONS Although Kenya has a large Aloe flora, the distributions of most taxa are restricted to sections of the country. Aloe secundiflora var. secundiflora was found to be both common and widespread; ten endemic taxa are known from less than three localities, while seven of them are micro-endemic. This study has identified criteria by which areas and taxa, respectively, should be prioritised for conservation of the genus Aloe in Kenya. The Aloe hotspots, which should be given the highest priority for the conservation of the genus in Kenya, roughly coincide with following areas: x Taita–Shimba Hills complex to the south-east x Naivasha–Baringo complex in the central Rift Valley x Kulal–Nyiru–Ndotos–Marsabit complex in the north. Of these areas, part of the Shimba hills is a nature reserve with a considerably high level of stability and protection. Although gazetted as a biosphere reserve the ecosystem health of Mount Kulal is generally on the decline with increasing loss of habitats (Quentin Luke, pers. com.). Similarly, most sections of the Taita Hills area and the Naivasha-Baringo hot spot occur on private land. In the absence of guaranteed regulation of land use, habitats in this area may be altered or destroyed without warning or consultation, thus putting Aloe populations at a risk of depletion. Although a considerable number of endemic taxa occur in remote areas (e.g. Mount Kulal) where anthropogenic threats to their survival are not immediate (Newton, 1995), general deterioration in the habitat is on the increase and hence the need for ecological monitoring and conservation intervention. With the various hot spots and important areas identified in this study, it seems feasible to adopt an ecosystem approach to the conservation of aloes in Kenya and the region as a whole.


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ACKNOWLEDGMENTS We would like to thank the East African Herbarium and herbarium at the Royal Botanic Gardens, Kew, for permission to study their Aloe collections; Salome Wabuyele for initial instruction in mapping and GIS software; Vegar Bakkestuen of NINA for providing base maps on Kenya and tutorials on the use of Arc View software; Dennis Malewa and Pius Namachanja of the NMK for providing digital maps of the flora area; Mathias Mbale for technical support in the field and herbarium in Kenya and Craig Hilton-Taylor (Cambridge) for help with the Red Listing process. This work was supported by grants from the Kenya Museum Society and the Norwegian Council of Universities’ Committee for Development and Education.

REFERENCES Baillie, J.E.M.B, C. Hilton-Taylor & S.N. Stuart (eds) (2004). 2004 IUCN Red List of Threatened Species: A global Species Assessment. IUCN, Gland & Cambridge. Beentje, H. & S. Smith (2001). FTEA and after. In E. Robbrecht, J. Degreef & I. Friis (eds), Plant Systematics and Phytogeography for the Understanding of African Biodiversity. Proceedings of the XVIth AETFAT Congress. Systematics and Geography of Plants 71(2): 265–290. Carter, S. (1994). Aloaceae. In R.M. Polhill (ed.), Flora of Tropical East Africa. A.A. Balkema, Rotterdam. CITES. (2006). CITES-listed Species Database. http://www.cites.org/eng/resources/species.html. Corsi, F., J. de Leeuw & A.K. Skidmore (2000). Modeling species distributions with GIS. In L.F. Boitani & T. Fuller (eds.), Research Techniques in Animal Ecology: Controversies and Consequences. Columbia University Press, New York. Cox B.C. & P.D Moore (2005). Biogeography: An Ecological and Evolutionary Approach. Blackwell Publishing, London. Fox, B.J. & M.D. Fox (2000). Factors determining mammal species richness on habitat islands and isolates: habitat diversity, disturbance, species interactions and guild assembly rules. Global Ecology and Biogeography 9: 19–37. Hepper, F.N. (1979). Second edition of the map showing the extent of floristic exploration in Africa south of the Sahara, published by AETFAT. In G. Kunkel (ed.), Taxonomic Aspects of African Economic Botany. Proceedings of the IX plenary meeting of AETFAT, Las Palmas de Gran Canaria. Pp. 157–162. Holland, P.G. (1978). An evolutionary biogeography of the genus Aloe. Journal of Biogeography 5: 227–238. Hopper, S.D. & P. Gioia (2004). The Southwest Australian Floristic Region: evolution and conservation of a global hot spot of biodiversity. Annual Review of Ecology and Systematics 35: 623–650. IUCN (2001). IUCN Red List Categories and Criteria: Version 3.1. IUCN Species Survival Commission, IUCN, Gland and Cambridge. KAWG (Kenya Aloes Working Group) (2004). Minutes of the meeting and launch of the Kenya Aloes Working Group held on 24 March 2004. Kenya Wildlife Service, Nairobi. Kihara, F.I., J.M Mathuva, M.G. Kamau & G. Mathenge. (2003). Aloe Trade in Kenya. Market Study Report. 64 + Appendices 131 pp. Laikipia Wildlife Forum, Nanyuki.

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Küper, W.J., H. Sommer, J.C. Lovett & W. Barthlott. (2006). Deficiency in African plant distribution data- missing pieces of the puzzle. Botanical Journal of the Linaean Society 150: 355–368. Lavranos, J. (1995). Aloaceae. In M. Thulin (ed.), Flora of Somalia Volume 4. Royal Botanic Gardens, Kew. Linder, H.P. (2001). Plant diversity and endemism in sub-Saharan tropical Africa. Journal of Biogeography 28: 168–182. Lovett J.C. & I. Friis (1996). Some patterns of endemism in the tropical north east and eastern African woody flora. In L.J.G. Van der Maesen, X.M. Van der Burgt & J.M. Van Medenbach de Rooy (eds), The Biodiversity of African Plants. Kluwer Academic Publishers, Dordrecht. Pp. 582–601. Lucas, G.L. (1968). Kenya. Acta Pytogeographica Suecica 54: 152–163. Marshall, N.T. (1998). Searching for a Cure: Conservation of Medicinal Wildlife in East and Southern Africa. TRAFFIC International, Cambridge. Mittermeier, R.A, P.R. Gil, M. Hoffman, J. Pilgrim, T. Brooks, C.G. Mittermeier, J. Lamoreux & G.A.B. da Fonseca (2005). Hotspots Revisited: Earths’s Biologically Richest and Most Threatened Terrestrial Ecoregions. Conservation International, Washington. Myers, N., R.A. Mittermeir, G.M. Cristina, G.A.B. da Fonseca & J. Kent (2000). Biodiversity hotspots for conservation priorities. Nature 403: 853–858. Newton, L.E (1995). Succulent plants in Kenya. Report to the British development division in Eastern Africa, in respect of a consultancy contract for the National Museums of Kenya Plant Conservation and Propagation Unit. Newton, L.E. (1996). Succulents and people in Africa. Aloe 33(24): 98–99. Newton, L.E. (2001). Aloe. In U. Eggli (ed.), Illustrated Handbook of Succulent Plants. Monocotyledons. Springer, Berlin. Pp. 103–186. Newton, L. E. (2004a) Aloes in habitat. In T. Reynolds (ed.), Aloes: The genus Aloe. CRC Press, Boca Raton. Pp. 3–14. Newton, L. E. (2004b). Succulent plant utilisation and conservation in eastern tropical Africa. In L. Russo (ed.), The Succulent Plants of Eastern Africa. Proceedings of the International Symposium: The Succulent Plants of Eastern Africa: History, Botanical Exploration and Research. Verbania 20–22 September 2004. Newton, L.E. (in press) Goodbye to the type locality of Aloe ballyi. CactusWorld. Nordal, I., Sebsebe Demissew & E.S. Odd (2001). Endemism in groups of geophytes (“Liliiflorae”). Biologiske Skrifter 54: 247–258. Nyamora, P. (1986). Medicinal plant given presidential protection. Daily Nation (Kenya) No. 8075 (22 November): 1, 24. Oketch, H.A. (1991). A Phytochemical Investigation of Three Species of Aloe Selected for Possible Commercial Exploitation. M.Sc. thesis, Kenyatta University, Nairobi. Peterson, A.T. & D.M. Watson (1998). Problems with areal definitions of endemism: the effects of spatial scaling. Diversity and Distributions 2: 189–194. Polhill, D. (1988). Flora of Tropical East Africa. Index of Collecting Localities. Royal Botanic Gardens, Kew. Reynolds G.W. (1966). Aloes of Tropical Africa and Madagascar. The Trustees, Aloe Book Fund, Mbabane. Reynolds, T. (1985). Observations on the phytochemistry of the Aloe leaf-exudate compounds. Botanical Journal of the Linnean Society 90: 179–199.


225

Reynolds, T. (1986). A contribution to the phytochemistry of the East African tetraploid shrubby aloes and their diploid allies. The Linnean Society of London 92: 383–392 Reynolds, T. (2004). Aloe chemistry. In T Reynolds (ed.), Aloes: The Genus Aloe. CRC Press, Boca Raton. Pp 41–74. Sebsebe Demissew, I. Nordal & O.E. Stabbetorp (2001). Endemism and patterns of distribution of the genus Aloe (Aloaceae) in the flora of Ethiopia and Eritrea. Biologiske Skrifter 54: 233–246. Viljoen, A.M., B.-E. Van Wyk & L.E. Newton (2001). The occurrence and taxonomical distribution of the anthrones aloin, aloinoside and microdontin in Aloe. Biochemical Systematics and Ecology 29: 53–67. Viljoen, A.M., B.-E. Van Wyk & F.R. Van Heerden (1998). Distribution and chemotaxonomic significance of flavonoids in Aloe (Asphodelaceae). Plant Systematics and Evolution 211: 31–42. Viljoen, A.M., B-E. Van Wyk & L.E. Newton (1999). Plicataloside in Aloe. A chemotaxonomic appraisal. Biochemical Systematics and Ecology 27: 507–517. White, F. (1983). The Vegetation of Africa. The United Nations Educational, Scientific and Cultural Organisation, Paris.